This research will be done primarily in Pecs, Hungary in collaboration with Dr. Gyorgy Szucs as an extension of NIH grant # RO1 AI4587-02 entitled "Moleculary Epidemiology and impact of human astroviruses". Astroviruses cause 2-17% of the diarrhea episodes that require medical care in children. Acute infectious gastroenteritis is one of the most important diseases in Hungary. A nationwide surveillance (1999) identified approximately 50,000 gastroenteritis episodes annually in the 10 million population of Hungary of which 52% were non-bacterial episodes. Of the non-bacterial gastroenteritis, 34% occur in children younger than 5 years of age. The parent grant focuses on the impact of human astroviruses (HastVs) among hospitalized children in a developed country (U.S.) and a community study among children in a developing country (Mexico). This study intends to characterize HAstVs in an Eastern European population (Hungary). Very little is known about HAstVs in this region. Active surveillance and the utilization of molecular epidemiology techniques developed in the parent grant for characterization of HAstVs should generate new understanding and possibly new reagents for the detection of HAstVs. This grant will infuse new methods, capabilities, and funding for research into an already productive collaboration. The hypotheses of this study are that HAstVs are a significant cause of acute gastroenteritis among children in Hungary and that clinical outcome in the country differs by genetic and/or antgenic types. The specific aims of this study are: 1. To determine frequency and genetic variability of HAstV strains among children hospitalized for gastroenteritis in Pecs, Hungary. 2. To determine the clinical characteristics of HAstV infection in children hospitalized for gastroenteritis in Hungary. 3. To measure the level of serum antibody in acute blood samples of children from symptomatic infections to determine the seroprevalence of HAstV type-specific antibodies. 4. To determine the burden of gastroenteritis associated with HAstV infection by evaluating the economic impact of severe HAstV diarrhea among children in one hospital over two years of surveillance.